Project Hasseu – Tutorial 1 – Programming a machine gun / projectile launcher

Welcome to the first tutorial as I develop Project Hasseu – programming a machine gun or projectile launcher, probably the core mechanic in shoot-em-up games. Below you see the the YouTube video to watch this tutorial, if not interested, the text based one is below!

Two pull this off you need two objects, the projectile (bullet) and the firing source (person, tower, etc.).

Bullet:
You first will need to attach a rigidbody to the bullet and then make it a prefab.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class BulletController : MonoBehaviour
{
    public float speed = 160f;
    public float bullet_spread = 0.01f;
    public Vector2 trajectory = new Vector2(0f,1f);
    private Rigidbody2D rb;
    private float distanceTravelled = 0f;
    public float maxDistance = 100f;

    // Start is called before the first frame update
    void Start()
    {
        // get rigidbody reference
        rb = this.GetComponent<Rigidbody2D>();
    }

    void FixedUpdate()
    {
        // get current position
        Vector2 currentPosition = rb.position;

        // move bullet by trajectory by speed and deltaTime
        rb.MovePosition(new Vector2(currentPosition.x + speed * trajectory.x * Time.deltaTime, currentPosition.y + speed * trajectory.y * Time.deltaTime));

        // running sum of distance travelled and destory if more than max distance
        distanceTravelled += speed * Time.deltaTime;
        if (distanceTravelled > maxDistance)
        {
            Destroy(this.gameObject);
        }
    }

    public void SetTrajectory(Vector2 trajectory)
    {
        // normalize so speed is not a function of trajectory magnitude
        trajectory.Normalize();

        // give some random spreading to bullet spray
        trajectory.x += Random.Range(bullet_spread, -1f * bullet_spread);
        trajectory.y += Random.Range(bullet_spread, -1f * bullet_spread);

        // saving trajectory to object
        this.trajectory = trajectory;

        // altering starting position of bullet with little magic to increase visual density (e.g. bullets not rendering at same distance each frame)
        float random = Random.Range(1f, 0f);
        this.transform.position +=  new Vector3(random * trajectory.x, random * trajectory.y, 0f);

        // converting trajectory into rotation angle and setting
        float angle = Mathf.Atan2(trajectory.y,trajectory.x)*360f/(2f*Mathf.PI)-90f;
        this.transform.rotation = Quaternion.Euler(0f,0f,angle);

    }
}

Player:
For the player I have attached a rigidbody and some code to move the player, but the core functionality is to get mouse input in the Update frame and execute the FireProjectile function.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerController : MonoBehaviour
{
    // reference to bullet prefab
    public GameObject bulletPreFab;

    // for movement variables
    private float horizontalInput;
    private float verticalInput;
    private float speed = 10f;
    private Rigidbody2D rigidbody;

    void Start()
    {
        rigidbody = this.GetComponent<Rigidbody2D>();
    }

    void Update()
    {
        // when mouse left button is down
        if (Input.GetMouseButton(0))
        {
            FireProjectile();
        }

        horizontalInput = Input.GetAxis("Horizontal");
        verticalInput = Input.GetAxis("Vertical");
    }

    void FixedUpdate()
    {
        rigidbody.MovePosition(rigidbody.position += new Vector2(speed * horizontalInput * Time.deltaTime, speed * verticalInput * Time.deltaTime));
    }

    private void FireProjectile()
    {
        // create the new bullet
        GameObject newObject = Instantiate(bulletPreFab);

        // setting starting position of bullet at character
        newObject.transform.position = this.transform.position;

        // direction to shoot (mouse coordinates - player)
        Vector2 trajectory = (Vector2)Camera.main.ScreenToWorldPoint(Input.mousePosition) - (Vector2)this.transform.position;

        // give trajectory to object
        newObject.GetComponent<BulletController>().SetTrajectory(trajectory);
    }
}

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